Benzimidazolocarbocyanine dyes



BENZHVHDAZOLOCARBOCYANINE DYES Leslie G. S. Brooker and Earl J. Van Lare, Rochester,

N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application August 23, 1954, Serial No. 451,696

14 Claims. (Cl. 260240.6)

This invention relates to carbocyanine dyes containing a substituted benzimidazole nucleus and methods for making them.

Symmetrical imidazolocarbocyanine dyes have been previously prepared. See Ogata--Proceedings of the Imperial Academy (Tokyo), volume 9 (1933), page 602.

We have now found a new class of carbocyanine dyes containing a substituted benzimidazole nucleus. The new dyes of our invention have been found to be particularly useful in altering the sensitivity of photographic silver halide emulsions. The sensitizing bands of our new dyes are unusually sharp, hence they can be used expeditiously in sensitizing photographic silver halide emulsions where little or no sensitivity in a given region of the spectrum is desired. They are also quite useful in supersensitizing combinations with other optical sensitizing dyes. See the copending application of Jean E. Jones, Serial No. 451,500, filed on even date herewith now U. S. Patent 2,751,296, issued June 19, 1956.

It is, therefore, an object of our invention to provide a new class of carbocyanine dyes. Another object is to provide methods for making these new dyes. Still another object is to provide photographic silver halide emulsions sensitized with our new dyes. Other objects will become apparent from a consideration of the following description and examples.

The new carbocyanine dyes of our invention can advantageously be represented by the following general formula:

wherein R represents an alkyl group, such as methyl, ethyl, n-propyl, n-butyl, allyl (vinylmethyl), carbethoxymethyl, etc. (e. g., an alkyl group containing from 1 to 4 carbon atoms), or an aryl group, such as phenyl, m-, or p-tolyl, etc. (e. g., a mononuclear aromatic group of the benzene series), R1 and R2 each represents an alkyl group, such as methyl, ethyl, n-propyl, n-butyl, allyl (vinylmethyl), carbethoxymethyl, etc. (e. g., an alkyl group containing from 1 to 4 carbon atoms), R3 represents an acetyl group, a RNHCO group, wherein R is a group identical to the R defined above, or a bromine atom, X represents an acid radical, such as chloride, bromide, iodide, perchlorate, thiocyanate, benzenesulfonate, p-toluenesulfonate, methylsulfate, ethylsulfate, etc., 12 represents a positive integer of from 1 to 2, and Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from 5 (n is 1) to 6 (n is 2) atoms in the heterocyclic ring, such as those of the thiazole series (e. g., thiazole, 4-methylthiazole, 4-phenylthiazo1e, S-methylthiazole, S-phenylthiazole, 4,5-dimethylthiazole, 4,5-diphenylthiazole, 4-(2 -thienyl)thiazo1e, etc.), those of nited States Patent 0 2,778,823 Patented Jan. 22, 1957 the benzothiazole series (e. g., benzothiazole, 4-chlorobenzothiazole, S-chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole, 4-rnethylbenzothiazole, 5- methylbenzothiazole, 6-methylbenzothiazole, S-bromobenzothiazole, 6-bromobenzothiazole, 4-phenylbenzothiazole, S-phenylbenzothiazole, 4-methoxybenzothiazole, 5- methoxybenzothiazole, 6-methoxybenzothiazole, S-iodobenzothiazole, 6-iodobenzothiazole, 4-ethoxybenzothiazole, S-ethoxybenzothiazole, tetrahydrobenzothiazole, 5,6- dimethoxybenzothiazole, 5,6-dioxymethylenebenzothiazole, S-hydroxybenzothiazole, 6-hydroxybenzothiazole, etc.), those of the naphthothiazole series (e. g., a-naphthothiazole, p-naphthothiazole, 5-methoxy-p-naphthiothia zole, 5-ethoXy-B-naphthothiazole, S-methoxy-a-naphthothiazole, 7-methoxy-wnaphthothiazole, etc.), those of the thianaphtheno-7',6,4,5-thiazole series (e. g., 4'-rnethoxythianaphtheno-7,6',4-5-thiazole, etc.), those of the oxazole series (e. g., 4-methyloxazole, S-methyloxazole, 4- phenyloxazole, 4,5-diphenyloxazole, 4-ethyloxazole, 4,5- dimethyloxazole, 5-phenyloxazole, etc.), those of the benzoxazole series (e. g., benzoxazole, S-chlorobenzoxazole, S-methylbenzoxazole, S-phenylbenzoxazole, 6-methylbenzoxazole, 5,6-dimethylbenzoxazole, 4,6-dimethylbenzoxazole, S-methoxybenzoxazole, S-ethoxybenzoxazole, 5-chlorobenzoxazole, 6-methoxybenzoxazole, 5- hydroxybenzoxazole, 6-hydroxybenzoxazole, etc.), those of the naphthoxazole series (e. g., a-naphthoxazole, [3- naphthoxazole, etc.), those of the selenazole series (e. g., 4-methylselenazole, 4-phenylselenazo1e, etc.), those of the benzoselenazole series (e. g., benzoselenazole, 5- chlorobenzoselenazole, S-methoxybenzoselenazolti, S-hydroxybenzoselenazole, tetrahydrobenzoselenazole, etc.), those of the naphthoselenazole series (e. g., a-naphthoselenazole, B-naphthoselenazole, etc.), those of the thiazoline series (e. g., thiazoline, 4-methylthiazoline, etc.), those of the Z-quinoline series (e. g., quinoline, 3-methylquinoline, S-methylquinoline, 7-methylquinoline, 8-methylquinoline, 6-chloroquinoline, 8-chloroquinoline, 6-methoxyquinoline, 6-ethoxyquinoline, 6-hydroxyquinoline, 8- hydroxyquinoline, etc.), those of the 4-quinoline series (e. g., quinoline, 6-methoxyquinoline, 7-methylquinoline, S-methylquinoline, etc.), those of the l-isoquinoline series (e. g., isoquinoline, 3,4-dihydroisoquinoline, etc.), those of the 3-isoquinoline series (e. g., isoquinoline, etc.), those of the benzimidazole series (e. g., 1,3-diethylbenzimidazole, 1-ethyl-3-phenylbenzimidazole, 1,3-diethyl- 5-ethylcarbamylbenzimidazole, S-acetyl-1,3-diethylbenzimidazole, S-bromo-1,3-diethylbenzimidazole, S-chloro- 1,3-diethylbenzimidazole, etc.), those of the 3,3-dialkylindolenine series (e. g., 3,3-dimethylindolenine, 3,3,5-trimethylindolenine, 3,3,7-trimethylindolenine, etc.), the pyridine series (e. g., pyridine, S-methylpyridine, etc.), etc.

The dyes of Formula I wherein R3 is an acetyl or ethylcarbamylgroup are particularly useful in practicing our invention.

According to our invention, we provide the symmetrical carbocyanine dyes embraced by Formula 1 above by condensing a compound selected from those represented by the following general formula:

II. R

wherein R, R1, R3, and X have the values given above, with chloral alcoholate. The condensations can advantageously be carried out in the presence of an inert diluent, such as the alcohol from which the alcoholate has been obtained. For example, inert diluents, such as ethanol, n-propanol, n-butanol, etc., can be employed. The condensations are advantageously carried out in the presence of a strong base, such as an alkali metal alcoholate, e. g., sodium ethylate, potassium ethylate, etc. Heat accelerates the condensations, although temperatures varying from room temperature (ca. 20 C.) to the reflux temperature of the reaction mixture can be employed.

The unsymmetrical carbocyanine dyes selected from those represented by Formula I can advantageously be prepared by condensing an'intermediate selected from those represented by Formula II with an intermediate selected from those represented by the following general formula:

III. Z

wherein R2, 11 and Z each have the values given above, X1 represents an acid radical, such as those listed above for X, for example, R4 represents a carboxylic acyl group, such as acetyl, propionyl, butyryl, isobutyryl, benzoyl, etc. (e. g., a carboxylic acyl group containing from 2 to 7 carbon atoms), and R5 represents an aryl group, such as phenyl, m-, or p-tolyl, etc. (e. g., a mononuclear aromatic group of the benzene series). The condensations can advantageously be effected in the presence of an inert diluent, such as the lower aliphatic alcohols (e. g., ethanol, n-propanol, isopropanol, n-butanol, etc.), pyridine, 1,4-dioxane, etc., and/or a basic condensing agent, such as the trialkylamines (e. g., triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, etc.), the N,N-dialkylanilines (e. g., N,N-dimethylaniline, N,N-diethylaniline, etc.), the N-alkylpiperidines (e. g., N-methylpiperidine, N-ethylpiperidine, etc.), etc. Heat accelerates the condensations, although temperatures varying from room temperature (ca. 20 C.) to the reflux temperature of the reaction mixture can ad vantageously be employed.

The following examples will serve to illustrate more fully the manner whereby we practice our invention.

Example 1 ,5 -diacetyl-1 ,1 ',3,3'-tetraethylbenzimidazolocarbocyanine iodide CHnCO- COCES Example 2.1,1',3,3'-tetraethyl-5,5'-di(ethylcarbamyl) benzimidazolocarbocyanine iodide CzH5NHCO -G ONHCzHs (i) 3115 C (H; I

To a solution of sodium ethylate, prepared from 0.6 g. (3 mols.) of sodium and 60 ml. of absolute ethyl alcohol, were added 3.87 g. (2 mols.) of 1,3-diethyl-5-ethylcarbamyl-Z-methylbenzimidazolium iodide and 1.0 g. (1 mol.) of chloral alcoholate. The reaction mixture was heated at the refluxing temperature for 30 minutes, chilled, filtered, and the residue was washed with water and dried. The yield of dye was 32 percent crude and 17 percent after two recrystallizations from absolute ethyl alcohol. The red crystals melted at 290292 C. with decomposition.

Example 3.5,5-dibr0m0-1,1',3,3tetraethylbenzimidazolocarbocyanine iodide To a solution of sodium ethylate, prepared from 0.6 g. (3 mols.) of sodium and 60 ml. of absolute ethyl alcohol,

were added 3.9 g. (2 mols.) of 5-bromo-l,3-diethyl-2- methylbenzimidazolium iodide and 1.0 g. (1 mol.) of chloral alcoholate. The reaction mixture was heated at the refluxing temperature for one hour, chilled, filtered, and the residue was washed with water and dried. The yield of dye was 38 percent crude and 28 percent after two recrystallizations from methyl alcohol. The red crystals with a bright-green reflex melted at 264-265 C. with decomposition.

Example 4.5-acetyl-1,3,3-triethylbenzimidazolo-oxacarbocyanine iodide C=CHOH=OHG 011300 i C2115 01155 I To a suspension of 1.8 g. (1 mol.) of 5acetyl-l,3- diethy1-2-methylbenzimidazolium iodide and 2.2 g. (1 mol.) of 2-l3-acetanilidovinyl-3-ethylbenzoxazolium iodide in 10 ml. of absolute ethyl alcohol was added 0.5 g. (1 mol.) of triethylamine. The reaction mixture was heated at the refluxing temperature for about one hour, chilled, filtered, and the residue was washed with a little ethyl alcohol and dried. The yield of dye was percent crude and 40 percent after two recrystallizations from ethyl alcohol. The minute red crystals melted at 230232 C. with decomposition.

Example 5.1,3,3'triethyl-5-etlzylcarbamylbenzimidazolooxacarbocyanine iodide This dye was obtained in the same manner as that of Example 4, by using 1.9 g. (1 mol.) of 1,3-diethyl-5-ethylcarbamyl-2-methy1benzimidazolium iodide instead of 5- acetyl-l,3-diethyl-2-methylbenzimidazolium iodide. The desired product was obtained in 37 percent yield after two recrystallizations from 50 percent aqueous alcohol, and the minute orange crystals melted at 94-96 C.

Example 6.5-bromo-l,3,3'-triethylbenzimidazolooxacarbocyanine iodide This dye was obtained in the same manner as that of Example 4, by using 2.0 g. (1 mol.) of 5bromo-1,3- diethyl-2-methylbenzimidazolium iodide, instead of 5- acetyl-l,3-diethyl-Z-methylbenzimidazolium iodide. The desired dye was obtained in 18 percent yield after two recrystallizations from ethyl alcohol, and the orange needles melted at 188-189 C. with decomposition.

Example 7.1,S-diethyZ-S-ethylcarbamyl-I ',3,3'-trimelh ylbenzimidazoloindocarbocyanine perchlorate Example 8.-5-acetyl 1,3-diethyl-1',3',3-trimethylbenzimidazoloindocarbocyanine perchlorate CgHs l (CH3): N

This dye was prepared in the same manner as that of Example 7, by using 1.8 g. (1 mol.) of 5-acetyl-1,3-dir ethyl-2-methylbenzimidazolium iodide, instead of 1,3-diethyl 5-ethylcarbamyl-2-methylbenzimidazolium iodide. The desired dye was obtained in 17 percent yield after two recrystallizations from absolute ethyl alcohol, and the red crystals with a golden reflex melted at 219-221 C. with decomposition.

Example 9.-5 bromo-1,3-diethyl-1 ',3',3'-trimethylbenzimidazoloindocarbocyanine perchlorate OZHE (ilzHfi This dye was prepared in the same. manner as that of Example 7, by using 2.0 g. (1 mol.) of -bromo-1,3-di- 6 ethyl-2-methylbenzimidaiolium iodide, instead of l,3-di= ethyl-5 ethylcarbamYl-Z-methylbenzimidazolium iodide. The desired dye was obtained in 19 percent yield after two recrystallizations from ethyl alcohol and the orange crystals melted at 231-233" C. with decomposition.

In preparing the unsymmetrical dyes of Examples 4-9, an intermediate selected from those represented by Formula III can be used wherein R4 represents a hydrogen atom, instead of an acyl group, provided a carboxylic anhydride, such as acetic anhydride, is present together with a basic condensing agent, such as triethylamine.

It has also been found that an intermediate selected from those'represented by Formula II above can be condensed with an intermediate selected from those reprewherein R4, R5, and n each have the values given above, and Q represents the non-metallic atoms necessary to complete a heterocyc-lic nucleus containing from 5 to 6 atoms in the heterocyclic ring, to produce merocyanine dyes. Intermediates of Formula IV which are suitable for this purpose have been described in Heseltine and Brooker U. S. Patent 2,666,761, issued January 19, 1954. Reaction conditions, such as those described above for the condensation of the compounds of Formula II with those of Formula III, can be employed for the condensation of the compounds of Formula H with those of Formula IV.

The following three examples describe the preparation of merocarbocyanine dyes.

Example 1 0.-5-[ (5-bromo-L3-diethyl-2 (3H -benzimidazolylidene -ethylidene] -3-ethylrhoa'anine ms- O=CH-OH=0 0:5 Br

Example 11 .5- (5-acetyl-1,3-diethyl-2 (3H) -benzimidazolylidene) ethylidene] -3-ethylrhodanine This dye was prepared in the same manner as that of Example 10, by using 1.8 g. (1 mol.) of 5-acetyl-1,3-diethyl-Z-methylbenzimidazolium iodide, instead of 5- bromo1,3-diethyl-2-methylbenzimidazolium iodide. The desired dye was obtained in 35 percent yield after two recrystallizations from ethyl alcohol, and the scarlet crystals melted at 231-233 C. with decomposition.

Example 12.-- (1,S-diethyl-5-ethylcarbamyl2(3H) benzimidazolylidene) ethylidene] -3-ethylrhodanine This dye was prepared in the same manner as that of Example 10, by using 1.9 g. (1 mol.) of 1,3-diethyl-5- ethylcarbamyl-Z-methylbenzimidazolium iodide, instead of S-bromo 1,3diethyl-Z-methylbenzirnidazolium iodide. The desired dye was obtained in 14 percent yield after two recrystallizations from methyl alcohol, and the minute orange crystals melted at 247-249" C. with decomposition.

The following examples describe the preparation of intermediates selected from those represented by Formula II above.

Example J3.-5-acetyl-1,3-zlietlzyl-2-methylbenzimidazolium iodide CgHg A mixture of 47 g. (1 mol.) of S-acctyl-l-ethyl-Z- methylbenzimidazole and 72.5 g. (1 mol. plus 50 percent excess) of ethyl iodide was heated at the refluxing temperature for 4 hours. The cake of crystals was broken up, ground to a line crystalline mass under acetone, filtered, and the residue was Washed with acetone. The yield was 47 percent. The colorless crystals from ethyl alcohol melted at 159-162 C. and decomposed at 202 C.

C sOO Example 14.1,3 diethyl-S-ethylcarbamyl-Z-methylbenzimid'azolium iodide CzEs CzHsNHC O Example 15.-5-l1r0mo-1 ,3-a'iethyl2-n'zerhylbenzimidazolium iodide C-CH: I Ja a A mixture of 60 g. (1 mol.) of S-bromo-Lethyl-Z- 8 methylhenzimidazole and 58.6 g. (1 mol. plus 50 percent excess) of ethyl iodide was heated at the refluxing temperature for 4 hours. After cooling, the product was collected on a filter and washed with acetone. The yield was 31 percent. The colorless crystals from ethyl alcohol melted at 240-242 C. with decomposition.

Example 16.-1-ethyl-5-ethylcarbamyl-2-methylbenzimidazole A solution of 106 g. (1 mol.) of N-ethyl-4-ethylamino-B-nitrobenzamide in 1 liter of glacial acetic acid and 195 g. (2 mols. plus 100 percent excess) of acetic anhydride was heated to C. and 185 g. (3 mols. plus percent excess) of zinc dust was added, with stirring, in small portions over a period of 15-20 minutes. During the addition of the zinc dust the temperature of the reaction mixture increased to the boiling point. Stirring and heating were continued at the refluxing temperature for 3 hours. The reaction mixture was filtered hot and the residue was washed with 500 ml. of hot acetic acid. The combined filtrate and washings was concentrated to a small volume. The residue was dissolved in 2 liters of water and the solution was made strongly alkaline with sodium hydroxide. After cooling, the alkaline solution was extracted with three SOO-ml. portions of chloroform. These extracts were combined and concentrated until all of the chloroform had been removed. The residue, on cooling and stirring, solidified. The yield was 68 percent. The almost colorless crystals from ethyl acetate melted at 157-158 C.

In like manner, S-acetyl-1-ethyl-2-methylbenzimidazole was obtained from 4-ethylarnino-3-nitroacetophenone. The residue, remaining after the chloroform had been removed, was distilled and the fraction boiling at 180- 200 C./2 mm. was used without further purification. The yield was 31 percent.

Similarly, S-bromo-1-ethyl-2-methylbenzimidazole was obtained from 4-bromo-N-ethyI-Z-nitroaniline. The residue remaining after the chloroform had been removed was cooled, filtered, and the residue was washed with a little ether. The combined filtrate and washings was fractionated. The fraction, which distilled at 175-200" C./8 mm. was used without further purification and the yield of this portion was 35 percent.

Example 17.-N-ethyl-4-ethylamin0-3-nitr0b nzamide NHCZH5 To g. (1 mol. plus 300 percent excess) of 70 percent aqueous solution of ethylamine was added, in small portions with shaking, 107 g. (1 mol.) of methyl 4- chloro-3-nitrobenzoate. During the addition of the ester the reaction mixture was cooled from time to time in a cold water bath. After the reaction mixture had stood 1 /2 hours at room temperature, it was heated at 40- 50 C. for 4 hours, then cooled, filtered, and the residue was Washed with water and dried. The yield was 95 percent. The pale-yellow crystals from ethyl alcohol melted at 131-134 C.

Example 18.4-ethylaminod-nilroacetophenone OHzO O N O:

To 260 g. (1 mol. plus 300 percent excess) of 70 percent aqueous solution of ethylamine was added, in small portions with shaking, 180 g. (1 mol.) of 4-chloro-3- nitroacetophenone. The temperature of the reaction mixture was kept below 40 C. by cooling in a water bath. Then the reaction mixture was heated 40-50 C. for 10 hours, diluted with water, chilled overnight, filtered and the residue was washed with water and dried. The yield was 84 percent. The yellow crystals from ethyl alcohol melted at 8486 C.

It is apparent that the position of the acetyl group, ethylcarbamyl group, and bromine atom on the' hem zimidazole ring can be varied, depending on the particular halogenated o-nitroaniline compound used as starting material. Also, the ethylamine of Examples 17 and 18 can be replaced with other primary amines, such as allylamine, n-propylamine, aniline, etc. to vary R in the intermediates selected from those represented by Formula II.

All of the dyes of our invention are particularly useful in manufacturing photographic silver halide emulsions, serving to alter the sensitivity thereof. Sensitization by means of our new dyes is, of course, directed primarily to the ordinarily employed, gelatino-silver-halide, developing-out emulsions. The dyes are advantageously incorporated in the washed, finished emulsion and should, of course, be uniformly distributed throughout the emulsion. In the preparation of photographic emulsions containing our new dyes, it is only necessary to disperse the dyes in the emulsions. The methods of incorporating dyes in emulsion are simple and well known to those skilled in the art of emulsion making. It is convenient to add the dyes from solutions in appropriate solvents. The solvent must, of course, be compatible with the emulsion and substantially free from any deleterious effect on the light-sensitive materials. Methanol has proven satisfactory as a solvent for the majority of our new dyes.

The concentration of our new dyes in the emulsion can vary widely, i. e. from about to about 100 mgs. per liter of flowable emulsion. The concentration of the dye will vary according to the type of light-sensitive material in the emulsion and according to the effects desired. The suitable and most economical concentration for any given emulsion will be apparent to those skilled in the art upon making the ordinary tests and observations customarily used in the art of emulsion making.

To prepare a gelatino-silver-halide emulsion sensitized with one or our new dyes, the following procedure is satisfactory: A quantity of the dye is dissolved in methyl alcohol or other suitable solvent and a volume of this solution (which may be diluted with water) containing from 5 to 100 mgs. of dye is slowly added to about 1000 cc. of a gelatino-silver-halide emulsion, with stirring. Stirring is continued until the dye is uniformly distributed throughout the emulsion. With most of our new dyes, to 20 mgs. of dye per liter of emulsion suffices to produce the maximum sensitizing effect with the ordinary gelatino-silver bromide (including bromiodide) emulsions. With fine-grain emulsions, which include most of the ordinarily employed gelatino-silver-chloride emulsions, somewhat larger concentrations of dye may be necessary to secure the optimum sensitizing etlect.

The above statements are only illustrative and are not to be understood as limiting our invention in any sense, as it will be apparent that our new dyes can be incorporated by other methods in many of the photographic silver halide emulsions customarily employed in the art. For instance, the dyes can be incorporated by bathing a plate or film upon which an emulsion has been coated, in the solution of the dye, in an appropriate solvent. Bathing methods, however, are not to be preferred ordinarily.

Photographic silver halide emulsions which can advantageously be sensitized by means of the new dyes of our invention comprise the customarily employed gelatinosilver-halide, gelatino-silver-chlorobromide, gelatino-silyer-bromide, and gelatino-silver-bromiodide developingout emulsions. v

Photographic silver halide emulsions, such as those listed above, containing the sensitizing dyes of our invention can also contain such addenda as chemical sensitizers, e. g.,sulfur sensitizers (e. g., allyl thiocarbamide, thiourea, allylisothiocyanate, cystine, etc.), various gold compounds (e. g., potassium chloroaurate, auric trichloride, etc.) (see U. S. Patents 2,540,085; 2,597,856 and 2,597,915), various palladium compounds, such as palladium chloride (U. S. 2,540,086), potassium chloropalladate (U. 8'. 2,598,079), etc., or mixtures of such sensitizers; anti-foggants, such as ammonium chloroplatinate (U. S. 2,566,245), ammonium chloroplatinite (U. S. 2,566,263), benzotriazole, nitrobenzimidazole, 5-nitroindazole, benzidine, mercaptans, etc. (see MeesThe Theory of the Photographic Process, Macmillan Pub., 1942, page 460), or mixtures thereof; hardners, such as formaldehyde (U. S. 1,763,533), chrome alum (U. S. 1,763,533), glyoxal (U. S. 1,870,354), dibromacrolein (Br. 406,750), etc., color couplers, such as those described in U. S. Patent 2,423,730, Spence and Carroll U. S. application 771,380, filed August 29, 1947 (now U. S. Patent 2,640,776), etc., or mixtures of such addenda. Dispersing agents for color couplers, such as those set forth in U. S. Patents 2,322,027 and 2,304,940, can also be employed in the above-described emulsions.

What we claim as our invention and desire secured by Letters Patent of the United States is:

1. A carbocyanine dye selected from those represented by the following general formula:

wherein R represents a member selected from the group consisting of an alkyl group containing from 1 to 4 carbon atoms and a mononuclear aromatic group of the benzene series containing from 6 to 7 carbon atoms, R1 and R2 each represents an alkyl group containing from 1 to 4 carbon atoms, R3 represents a member selected from the group consisting of an acetyl group and a --NHCO group wherein R represents an alkyl group containing from 1 to 4 carbon atoms, X represents an acid radical, n represents a positive integer of from 1 to 2, and Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of those of the thiazole series, those of the benzothiazole series, those of the naphthothiazole series, those of the thianaphtheno-7,6,4,5-thiazole series, those of the oxazole series, those of the benzoxazole series, those of the naphthoxazole series, those of the selenazole series, those ,of the benzoselenazole series, those of the naphthoselenazole series, those of the Z-quinoline series, those of the 4-quinoline series, those of the l-isoquinoline series, those of the 3-isoquinoline series, those of the benzimidazole series, those of the 3,3-dialkylindolenine I series, and those of the pyridine series.

2. A carbocyanine dye selected from those represented by the following general formula:

wherein R and R1 each represents an alkyl group containing from 1 to 4 carbon atoms and X represents an acid radical.

1 1 3. A carbocyanine dye selected from those represented by the following general formula:

wherein R and R1 each represents an alkyl group containing from 1 to 4 carbon atoms and X represents an acid radical.

4. A carbocyanine dye selected from those represented by the following general formula:

wherein R, R1 and R2 each represents an 'alkyl group containing from 1 to 4 carbon atoms and X represents an acid radical.

5. A carbocyanine dye selected from those represented by the following general formula:

wherein R, R1 and R2 each represents an alkyl group containing from 1 to 4 carbon atoms and X represents an acid radical.

6. A carbocyanine dye selected from those represented by the following general formula:

wherein R, R1 and R2 each represents an alkyl group containing from 1 to 4 carbon atoms and X represents an acid radical.

7. The carbocyanine dye having the folio-wing formula:

8. The carbocyanine dye having the following formula:

. 9. vThe carbocyanine. dye having the following formula:

OQHE

10. The carbocyanine dye having the following formula:

11. The carbocyanine dye having the following formula:

OHaC O- 12. A process for preparing. carbocyanine dyes comprising condensing a compound selected from those represented by the following general formula:

wherein R represents a member selected from the group consisting of an alkyl group containing from 1 to 4 carbon atoms and a mononuclear aromatic group of the henzene series containing from 6 to 7 carbon atoms, R1 represents an alkyl group containing from 1 to 4 carbon atoms, R3 represents a member selected from the group consisting of an acetyl group and an R'NHCO- group wherein R represents an alkyl group containing from 1 to 4 carbon atoms, and X represents an acid radical, together with a compound selected from those represented by the following general formula:

wherein R2 represents an alkyl group containing from 1 to 4 carbon atoms, Re represents a carboxylic acyl group containing from 2 to 7 carbon atoms, R5 represents a mononuclear aromatic group of the benzene series containing from 6 to 7 carbon atoms, X1 represents an acid radical, n represents a positive integer of from 1 to 2, and Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring selected from. the grou consisting of those of the thiazole series, those of the benzothiazole series, those of the naphthothiazole series, those of the thianaphtheno-7',6',4,5-thiazole series, those of the oXazole series, those of the benzoxazole series, those of the naphthoxazole series, those of the selenazolc series, those-of the benzoselenazole series, those of the naphthoselenazole series, those of the Z-quinoline series, those of the 4-quinoline series, those of the l-isoquincline series, those of the 3-isoquinoline series, those of the benzimidazole series, those of the 3,3-dialkylindolenine References Cited in the file of this patent series, and those of the pyridine series. UNITED STATES PATENTS 13. A process according to clalm 12 wherein the con- 5 densation is carried out in the presence of a basic con- Kumetat 1941 (lensing agent 5 2,354,524 Kumetat July 25, 1944 14. A process according to claim 13 wherein the basic 2701198 Carroll 1955 condensing agent is triethylamine. FOREIGN PATENTS 845,876 France 1939 

1. A CARBOCYANINE DYE SELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 